# Comparison of Cooling System Designs for an Exhaust Heat Recovery System Using an Organic Rankine Cycle on a Heavy Duty Truck

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## Abstract

**:**

## 1. Introduction

_{2}limits. Current truck engines have a thermal efficiency of up to 46%, and conventional possibilities to further improve this efficiency are limited and costly.

## 2. Description of the Vehicle Setup

^{−1}, 1500 Nm), and compares steady state engine test bench data to averaged road data.

## 3. Description of the Simulation Model

#### 3.1. Exhaust Evaporator Model

#### 3.2. Exhaust Gas Recirculation Evaporator Model

#### 3.3. Condenser Model

#### 3.4. Expander Model

#### 3.5. Working Fluid Pump Model

#### 3.6. Split Valve Model

#### 3.7. Radiator Model

^{−1}. Slip losses of the viscous clutches were included.

#### 3.8. Charge Air Cooler Model

#### 3.9. Air Flow through the Radiator Package and Fan Model

#### 3.10. Thermostat Model

#### 3.11. Thermal Engine Model

#### 3.12. Solver

## 4. Description of the Control Strategy

#### 4.1. Working Fluid Pump (Rotational Speed)

#### 4.2. Working Fluid Split Valve (Position)

#### 4.3. Expansion Device (Rotational Speed)

#### 4.4. Exhaust Flap (Position)

#### 4.5. Expander Bypass Valve (Position)

#### 4.6. Condenser Coolant Pump (Speed)

#### 4.7. Coolant Valve (Position)

#### 4.8. Fan and Engine Coolant Pump

## 5. Simulation Results

#### 5.1. Steady State Simulation

#### 5.2. Full Transient Simulation

## 6. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## Abbreviations

EGR | Exhaust gas recirculation |

EGA | Exhaust gas after-treatment |

EHR | Exhaust heat recovery |

ECU | Electronic control unit |

ORC | Organic Rankine Cycle |

PID | Proportional-integral-derivative |

CAC | Charge air cooler |

## Formula Symbols

$\mathsf{\alpha}$ | Heat transfer coefficient |

$Re$ | Reynolds number |

$Pr$ | Prandtl number |

$k$ | Conductivity |

$D$ | Reference length |

$\mathsf{\rho}$ | Density |

$v$ | Velocity |

$x$ | Steam quality |

${\ast}_{liq}$ | In liquid phase |

${\ast}_{vap}$ | In vapor phase |

$Nu$ | Nusselt number |

$C$ | Nusselt coefficient |

$m$ | Nusselt exponent |

$p$ | Pressure |

$z$ | Length |

$\dot{V}$ | Volume flow |

$\mathsf{\omega}$ | Rotational speed |

${V}_{i}$ | Expander inlet volume |

${\mathsf{\eta}}_{vol}$ | Volumetric efficiency |

${P}_{i}$ | Indicated power |

${\mathsf{\eta}}_{i}$ | Isentropic efficiency |

$\Delta h$ | Isentropic enthalpy drop across turbine |

$\dot{m}$ | Mass flow |

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**Figure 1.**Parallel evaporator Rankine cycle. EGA: exhaust gas after-treatment; EGR: exhaust gas recirculation; and EHR: exhaust heat recovery.

**Figure 5.**Ethanol and exhaust evaporator outlet temperature, comparison of test bench measurement and simulation results (dashed lines: ±10 K) [18].

**Figure 11.**Simplified control strategy flow chart (vapor cycle only). PID: proportional-integral-derivative controller.

**Table 1.**Comparison of road average and steady state test bench boundary conditions, operating point 3. EGA: exhaust gas after-treatment; and EGR: exhaust gas recirculation.

Parameter | Road Average | Test Bench |
---|---|---|

Engine speed (1/min) | 1239 | 1239 |

Engine torque (Nm) | 1486 | 1486 |

EGA temperature (°C) | 278.9 | 390.7 |

EGR temperature (°C) | 460.3 | 538.8 |

EGA mass flow (kg/s) | 0.242 | 0.240 |

EGR mass flow (kg/s) | 0.067 | 0.073 |

Parameter | Floating Temperature Approach | Low Temperature Approach | ||||||||
---|---|---|---|---|---|---|---|---|---|---|

Operating point | 1 | 2 | 3 | 4 | 5 | 1 | 2 | 3 | 4 | 5 |

Expander power (kW) | 2.79 | 4.36 | 5.24 | 6.50 | 8.60 | 2.76 | 4.40 | 6.02 | 8.32 | 10.7 |

Condensation pressure abs. (bar) | 0.94 | 1.03 | 1.90 | 2.80 | 3.00 | 0.93 | 0.95 | 0.98 | 1.01 | 1.10 |

Feed pump power (kW) | 0.08 | 0.12 | 0.18 | 0.30 | 0.50 | 0.08 | 0.12 | 0.17 | 0.29 | 0.49 |

Boiling pressure abs. (bar) | 11.1 | 12.5 | 14.0 | 16.6 | 20.1 | 11.1 | 12.2 | 13.0 | 16.1 | 19.5 |

Condenser coolant pump power (kW) | 0.02 | 0.09 | 0.48 | 0.48 | 0.48 | 0.02 | 0.04 | 0.08 | 0.09 | 0.46 |

Fan speed (1/min) | 160 | 160 | 160 | 394 | 683 | 160 | 160 | 160 | 342 | 615 |

Condenser coolant temperature (°C) | 60.0 | 67.0 | 86.7 | 97.1 | 97.1 | 60.0 | 60.0 | 60.0 | 60.0 | 65.4 |

Power gain (%) | 3.89 | 3.18 | 2.37 | 2.10 | 2.41 | 3.85 | 3.25 | 2.99 | 2.92 | 3.07 |

Overall power gain/fuel consumption improvement (%) | 2.52 | 3.09 |

Parameter | Floating Temperature Approach | Low Temperature Approach | ||||||||
---|---|---|---|---|---|---|---|---|---|---|

Operating point | 1 | 2 | 3 | 4 | 5 | 1 | 2 | 3 | 4 | 5 |

Expander power (kW) | 2.72 | 4.06 | 5.41 | 6.93 | 8.56 | 2.96 | 4.44 | 5.88 | 7.82 | 9.97 |

Condensation pressure abs. (bar) | 1.34 | 1.47 | 1.56 | 1.99 | 2.86 | 0.92 | 0.97 | 1.03 | 1.14 | 1.46 |

Feed pump power (kW) | 0.08 | 0.13 | 0.19 | 0.31 | 0.51 | 0.08 | 0.13 | 0.19 | 0.30 | 0.49 |

Boiling pressure abs. (bar) | 11.6 | 12.6 | 13.5 | 15.9 | 19.7 | 11.2 | 12.2 | 13.1 | 15.6 | 19.2 |

Condenser coolant pump power (kW) | 0.17 | 0.23 | 0.25 | 0.37 | 0.45 | 0.05 | 0.08 | 0.12 | 0.21 | 0.39 |

Fan speed (1/min) | 172 | 170 | 170 | 244 | 470 | 171 | 169 | 170 | 234 | 401 |

Condenser coolant temperature in (°C) | 73.9 | 77.0 | 77.5 | 84.8 | 95.8 | 60.4 | 60.7 | 61.1 | 63.6 | 71.9 |

Power gain (%) | 3.56 | 2.83 | 2.57 | 2.30 | 2.41 | 4.09 | 3.23 | 2.88 | 2.68 | 2.88 |

Overall power gain/fuel consumption improvement (%) | 2.63 | 3.07 |

© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).

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**MDPI and ACS Style**

Stanzel, N.; Streule, T.; Preißinger, M.; Brüggemann, D.
Comparison of Cooling System Designs for an Exhaust Heat Recovery System Using an Organic Rankine Cycle on a Heavy Duty Truck. *Energies* **2016**, *9*, 928.
https://doi.org/10.3390/en9110928

**AMA Style**

Stanzel N, Streule T, Preißinger M, Brüggemann D.
Comparison of Cooling System Designs for an Exhaust Heat Recovery System Using an Organic Rankine Cycle on a Heavy Duty Truck. *Energies*. 2016; 9(11):928.
https://doi.org/10.3390/en9110928

**Chicago/Turabian Style**

Stanzel, Nicolas, Thomas Streule, Markus Preißinger, and Dieter Brüggemann.
2016. "Comparison of Cooling System Designs for an Exhaust Heat Recovery System Using an Organic Rankine Cycle on a Heavy Duty Truck" *Energies* 9, no. 11: 928.
https://doi.org/10.3390/en9110928